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'[ot]: IR paper detector for a shredder'
2001\03\11@232622 by rad0

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my shredder jammed and I discovered that the paper detector
had been mangled and broke from its mount.

This detector seems to be two clear led's fixed in a mount
pointing down form above the paper slot at about a 45 degree
angle, like a 'V'

Question is, how does this thing work?  It looks to me like two
clear led's, how does it detect anything?


Thanks...

one of the led's is broken and I was wondering if I could just
replace it, and have the thing work...

I don't see how it detects anything.

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2001\03\12@042703 by Alan B. Pearce

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it will not be two LEDs, but rather an LED and a detector diode. I would try
replacing it with a standard opto interrupter type unit, which it may well be
anyway.

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2001\03\12@095822 by Chris Carr

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I think that you will find that one is and LED and the other is an
opto-receiver.
The light from the LED (could be infra-red) reflects off the paper to cause
the opto-receiver to conduct operating a relay, triac and turning on the
motor. With no paper there is not sufficient reflected light so motor is
switched off.

Regards
Chris

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2001\03\12@101239 by Lawrence Lile

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Most likely one of the items is really a phototransistor.  These often come
in packages that are exactly like LED's.  The other is most likely an IR
LED.  You could probably distinguish them out of circuit by placing 5 v
through 2000 ohms on the terminals -

With the LED, with one polarity you will drop about 1.5 volts across the
LED.  If it is IR, you won't be able to see it lit up.  Reverse biased it
will be an open circuit.

With the phototransistor, you will have a much smaller voltage drop if it is
exposed to any light.  In dark, it will be an open circuit.   Reverse biased
it will be an open circuit.

You could probably replace these, once you figure out which is which, with
any IR-LED and phototransistor pair say from Radio Shark.  At any rate, it
is worthwhile hacking them, because LED/phototransistor detectors are very
common, and useful to understand.

Good Luck!

--Lawrence Lile



{Original Message removed}

2001\03\12@104202 by Ben Suffolk

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One of the LEDs will be an emitter, the other a sensor.

Regards

Ben

To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
cc:
From: rad0 <rden25spamspam_OUTMINDSPRING.COM>
Subject: [ot]: IR paper detector for a shredder

Question is, how does this thing work?  It looks to me like two
clear led's, how does it detect anything?



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2001\03\12@111810 by Russell Farnhill

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Hi,

Iam guessing one will be an infra-red emitter and the other a detector.
This sensor simply relies on the IR beam being reflected back into the
detector
by the sheet of paper, also these usually have an operating range of about
10mm (just guessing here) because of the 45Deg angle. I've seen ready made
detector like these from most suppliers. Also if you fit a new one you may
find you have to adjust a trim pot somewhere as these usually need
calibrating
as paper colour etc can affect performance, at least on the scanners and
jukebox's
I work on this needs to be done.

cheers,

Russ.

{Original Message removed}

2001\03\12@112455 by Bob Blick

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Probably one is an LED and the other a phototransistor.

-Bob

On Mon, 12 Mar 2001, rad0 wrote:

> my shredder jammed and I discovered that the paper detector
> had been mangled and broke from its mount.
>
> This detector seems to be two clear led's fixed in a mount
> pointing down form above the paper slot at about a 45 degree
> angle, like a 'V'

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2001\03\12@114801 by Herbert Graf

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> my shredder jammed and I discovered that the paper detector
> had been mangled and broke from its mount.
>
> This detector seems to be two clear led's fixed in a mount
> pointing down form above the paper slot at about a 45 degree
> angle, like a 'V'
>
> Question is, how does this thing work?  It looks to me like two
> clear led's, how does it detect anything?

    My guess is that it isn't two LEDs but instead one IR LED and one IR
phototransitor. The reflection difference between paper and no paper is what
it detects. These should be pretty standard parts, hardest part in you're
case is figuring out whether the LED or the phototransistor is damaged. TTYL

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2001\03\12@122731 by rad0

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thanks very much,

they look identical, how do you tell one from the other??



----- Original Message -----
From: "Alan B. Pearce" <spamBeGoneA.B.PearcespamBeGonespamRL.AC.UK>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Monday, March 12, 2001 3:26 AM
Subject: Re: [ot]: IR paper detector for a shredder


> it will not be two LEDs, but rather an LED and a detector diode. I would
try
> replacing it with a standard opto interrupter type unit, which it may well
be
> anyway.
>
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2001\03\12@123605 by Alan B. Pearce

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>they look identical, how do you tell one from the other??

There is normally an indicator on the case to indicate + and - for the LED, and
possibly E and C for the transistor. These markings are often moulded into the
case rather than printed on.

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2001\03\12@141329 by mike

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On Mon, 12 Mar 2001 10:25:34 -0600, you wrote:

>my shredder jammed and I discovered that the paper detector
>had been mangled and broke from its mount.
>
>This detector seems to be two clear led's fixed in a mount
>pointing down form above the paper slot at about a 45 degree
>angle, like a 'V'
>
>Question is, how does this thing work?  It looks to me like two
>clear led's, how does it detect anything?
One of them is not a LED - it's either a photodiode or phototransistor
in a LED style package.
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2001\03\12@173813 by Jinx

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> >they look identical, how do you tell one from the other??
>
> There is normally an indicator on the case to indicate + and -
> for the LED, and possibly E and C for the transistor. These
> markings are often moulded into the case rather than printed
> on

I've had the odd one with no markings, in which case it's trial
and error. You can find which is which (and the polarity of the
emitter, a diode) with an ohmmeter. For 5V operation put a
220R resistor in series with the emitter and ground the other
side. The polarity of the detector may not be obvious. Put a
10k resistor in series with it and ground the other side. 5V goes
to the other end of the 10k resistor. If you got it right (50/50
chance), you'll see the voltage at the 10k/detector pin junction
dip when you point the opto at a piece of white paper. If nothing
happens reverse the connections to the detector

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2001\03\12@183348 by James R Albers

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Hello,

I had the unfortunate task of repairing paper shredders for a number of
years.  What you describe is an infrared detector pair.  One led is an
infrared emitter and the other is a photo transistor detector.  The paper
going through the machine provides a reflective surface (white paper is
about 80% reflective) and the infrared photo transistor detects the
reflected infrared that is emitted by the led.  You should be able to use
any readily available infrared led/photo transistor, assuming it will
fit.  The infrared led may be fed directly from the power supply (with
limiting resistor) assuming it is not "chopped".

Jim Albers

On Mon, 12 Mar 2001 10:25:34 -0600 rad0 <RemoveMErden25TakeThisOuTspamspamMINDSPRING.COM> writes:
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2001\03\12@184439 by rad0

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Thanks Jim,

I'm going to machine a little block of aluminium
and drill some holes at a 45 degree angle and
put some silicon into the hole to hold the led/pair

this ought to fix it

one lead on one led is broken and I should be able to solder
it back together, the plastic mounting case was destroyed...


Thanks all...


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